Geochemical responses in peat groundwater over Attawapiskat kimberlites, James Bay Lowlands, Canada and their application to diamond exploration

ABSTRACT Peat groundwater compositions at depths of 0.4 and 1.1 m below ground surface in the Attawapiskat region of the James Bay
Lowlands are evaluated for diamond exploration applications. Samples were collected along transects that typically extended
at least 200 m beyond the margins of Yankee, Zulu, and Golf kimberlites. Locations of upwelling groundwater usually occur
at or near kimberlite margins based on hydrogeological measurements and variations in peat groundwater geochemical parameters
(pH and EC are high, and the Eh is low relative to ombrotrophic peat groundwaters). Concentrations of the kimberlite pathfinder
metals Ni, Cr, light rare earth elements (LREEs), Ba, Mg/Ca, and alkalis are commonly elevated at sample sites at or near
kimberlite margins and where groundwaters are upwelling. The presence of elevated kimberlite pathfinders at these sites suggests
that fractures along the boundaries between kimberlites and limestone formed during kimberlite emplacement provide dilation
for upward movement of groundwater with elevated kimberlite pathfinder metals. Typically, Ni, Cr, LREE, and Ba behave similarly
and thus high concentrations of these metals are found at similar locations along transects. On the other hand, locations
of elevated alkalis and Mg/Ca vary. The spatial variations among pathfinder metals in peat groundwaters are possibly due to
geochemical processes in the peat, such as metal binding to dissolved organic material, adsorption to insoluble organics or
Fe-oxyhydroxides, and incorporation into secondary mineral precipitates, which can act to increase or decrease metal solubility.
The findings of this study are readily applicable in diamond exploration in wetlands elsewhere.

摘要：本研究评估了詹姆斯湾低地阿塔瓦皮斯卡特地区地表以下0.4米和1.1米深度的泥炭地下水组成，以评估其在钻石勘探应用中的适用性。样品采集于横跨 Yankee、Zulu 和 Golf 金伯利岩边缘的横断面，通常延伸至金伯利岩边缘以外至少200米。根据水文地质测量和泥炭地下水地球化学参数（如pH和电导率较高，而Eh相对较低，相对于淋溶泥炭地下水而言）的变化，地下水涌升通常发生在金伯利岩边缘或附近。在金伯利岩边缘附近和地下水涌升处，金伯利岩指示性金属（如Ni、Cr、轻稀土元素（LREEs）、Ba、Mg/Ca和碱金属）的浓度通常较高。这些地点金伯利岩指示性金属的富集表明，金伯利岩与石灰岩边界形成的裂缝在金伯利岩形成过程中提供了地下水向上移动的空间。通常，Ni、Cr、LREE和Ba的行为相似，因此在横断面上的相似位置可以发现这些金属的高浓度。另一方面，碱金属和Mg/Ca的升高位置有所不同。泥炭地下水中指示性金属的空间变化可能源于泥炭中的地球化学过程，例如金属与溶解有机物质结合、吸附于不溶性有机物或Fe-氧水化物上，以及进入次生矿物沉淀中，这些过程可以增加或降低金属的溶解度。本研究的结果易于应用于其他湿地的钻石勘探。